1. Technical Field
Example embodiments of the present invention relate in general to a wireless sensor network and more specifically to a wireless sensor network system, a method for placing a plurality of sensor nodes in a wireless sensor network system, and a method for computing sensing energy consumption per area of a plurality of sensor nodes.
2. Description of the Related Art
A wireless sensor network having a plurality of sensor nodes such as a ubiquitous sensor network is widely used. A wireless sensor network is configured such that a plurality of sensor nodes are densely deployed and are connected by a wireless interface.
A sensor node in a wireless sensor network system performs tasks which collect data, aggregate data and transmit data. In most cases, the tasks require much more energy than a task which processes data at other network node (data processing node). For this reason, it is a main issue of a wireless sensor network system how to reduce the amount of energy consumed when a sensor node performs tasks.
The energy consumption optimization has been researched based on two approaches. A first approach is to perform scheduling to activate some of sensor nodes, and a second approach is to adjust a sensing range to reduce redundant energy consumption.
In case of the second approach, it is very important how to place sensor nodes when seen in a two-dimensional plane and how to set a sensing range of each sensor node.
Each sensing area range has to be optimally set to minimizes the overlap of the sensing areas and to prevent an occurrence of a gap area which does not belong to any sensing area range. Conventionally, research has been conducted under the assumption that all sensor nodes have the same sensing area range, but the assumption has a limitation to reducing a gap area.
Meanwhile, in order to set an optimum sensing range, it is necessary to compute sensing energy consumption per area (“SECPA”). According to a conventional SECPA computation technique, a tile area is defined by connecting adjacent sensor nodes, and energy consumption within the tile area is computed. The tile area has many overlap areas that sensor nodes overlap each other. However, the conventional SECPA computation technique has an error factor since it considers only the whole sensing area but does not consider overlap areas in which sensor nodes overlap each other. This has an influence on setting of an optimum sensing area range.
A conventional SECPA computation is described in an article by J. Wu and S. Yang (J. Wu and S. Yang, “Energy-Efficient Node Scheduling Models in Sensor Networks with Adjustable Ranges”, International Journal of Foundations of Computer Science, Vol. 16, No. 1, 2005 3-17).